"TCAS sometimes causes problems. A reported airprox (an event in which two aircraft come too close to each other) over Trasadingen in Switzerland in 2000 was triggered through excessive pilot reactions to TCAS advisories (it is an advisory system: any responsive actions are still human), and the report has just come out about an incident on 16 November 2006 over South Korea, in which the pilot's maneuver in response to an advisory was violent enough to injure 20 people on board his aircraft, four of them seriously. (Anecdotes and reports abound of “excessive” reactions.)"
That is not TCAS causing problems, that is pilots causing problems by not following proper procedures just like in the midair over Germany. In that midair and in the excessive manouvering incidents, TCAS worked as advertised.